1. Field of the Invention
The present invention relates to a sheet processing system that performs predetermined post-processing on sheets (the sheets include recording sheets and transfer sheets) and sheet members, such as OHP transparencies, (hereinafter, “sheets”), a sheet-supply control method that is performed by the sheet processing system, and a computer program product for causing a computer to perform the sheet-supply control method.
2. Description of the Related Art
Japanese Patent Application Laid-open No. H9-255219 and Japanese Patent Application Laid-open No. 2002-273705 disclose typical sheet processing devices each of which includes a post-processing unit that performs predetermined post-processing on sheets. A stapler unit according to the invention disclosed in Japanese Patent Application Laid-open No. H9-255219 includes a stapling unit and a staple receiving unit as separate units, each of which can individually move to a stapling position, which allows for providing a finisher with easy handling while providing a capability to staple various types of sheets and maintain a high copy rate. When “staple empty”, which is indicative of a shortage of staples within the staple unit, is detected, the stapling unit returns to a staple replacement position (home position). When a staple jam is detected, the staple receiving unit moves back to a retraction position (home position).
The sheet processing device according to the invention disclosed in Japanese Patent Application Laid-open No. 2002-273705 includes a stapler that is designed in such a manner that a user can manually rotate the stapler only when the stapler is in a position to have its staple cartridge replaced (hereinafter, “staple replacement position”). The sheet processing device includes a unit that moves the stapler along the trailing edge of the sheet with respect to the sheet conveying direction; a unit that supports the stapler in such a manner that the stapler cannot rotate when the stapler is moving along the trailing edge with respect to the sheet conveying direction, while the stapler can rotate at a predetermined position; and a unit that controls the angle that the stapler rotates at the predetermined position. Because the predetermine position corresponds to the staple replacement position, the stapler can rotate only when in the staple replacement position. This improves the efficiency of the staple replacement activity.
It follows that, in a conventional image processing system that includes an image forming apparatus and the above-described sheet processing device (sheet post-processing device) connected to each other, when staple empty (indicative of a shortage of items used in the sheet post-processing device) is detected, the stapler is moved to the staple replacement position so that the user can promptly perform the staple filling operation. Moreover, because the stapler can rotate only when in the staple replacement position, the efficiency of the staple replacement operation is improved.
According to the above-described conventional technology, if staple empty is detected and the stapler is moved to the staple-filling position, actions concerning the stapling process are basically prevented until the stapler is filled with new staples; however, there are cases where it is preferable to keep performing the stapling process under this staple-empty situation. In most cases, notification of staple empty is made when a small number of staples still remain. This is because even after the sheet post-processing device notifies the image forming apparatus of staple empty, because the flow of sheets that have already been subjected to the image processing cannot be stopped, the stapling process needs to be performed several more times and sometimes more than ten times. Therefore, notification of staple empty is made when several tens of staples still remain.
This means that, even after the stapler is moved to the staple-filling position, it is possible to perform the stapling process several tens of times before filling it with new staples. If the stapling process cannot be suspended because of processes performed by the image forming apparatus or if the user needs several stapled sets urgently, it is possible to temporarily permit the actions concerning the stapling process with the risk of the stapler actually becoming staple empty.
Moreover, if staple empty is detected in the course of the stapling process with several sets remaining unprocessed, although, in principal, the stapling process stops temporarily and resumes after the stapler is filled with new staples, if the user cannot perform the staple filling operation immediately, it is possible to continue only the image formation without performing the stapling process before the stapler is filled with new staples. In this case, the user will make an instruction to resume the stapling process later. If the stapling process is not needed, some sheet processing devices can operate even if the stapler is in the staple-filling position; however, the sheet processing devices may not align the sheets precisely when the stapler is in the staple-filling position. In most cases, notification of either “stapling” or “discharge without stapling” has not been made at the start of the first process on the sheet set.
As described above, after notification of staple empty is made and the stapler is moved to the staple-filling position, notification of a stapling resume request (including a request for discharge without stapling) is made, in some cases. If the notification of the stapling resume request is made at the start of the process, the sheet processing device first moves the stapler to a predetermined position depending on the mode of stapling and the sheet size and then receives the sheet. However, the stapler-filling position is set to such a position that the stapler first moves to the normal stapler home position and then moves to the staple-filling position. In the invention disclosed in Japanese Patent Application Laid-open No. 2002-273705, after the stapler is moved to this position, the stapler is rotated so that the user can easily perform the staple replacement from the front side of the sheet post-processing device.
In this case, to move the stapler to the stapling position, it is necessary to rotate the stapler to the previous angle and then move the stapler to the predetermined position. Therefore, it takes a longer time to move the stapler to the stapling position compared with the usual case. That is, the interval increases between when the post-processing device receives notification of the post-processing mode and the sheet size or the like from the image forming apparatus and when the sheet post-processing device is ready to receive the sheet.
Because the time to set the sheet post-processing device ready to receive the sheet is necessary, when the sheet is supplied from the image forming apparatus to the sheet post-processing device, it is necessary for the image forming apparatus to notify the sheet post-processing device of the selected post-processing mode and supply the sheet a specified time Tw after. If the moving of the stapler from the staple-filling position is taken into consideration, there is the necessity to set the specified time Tw to the time that the stapler requires to move from the staple-filling position; therefore, it takes a longer time than usual. In this case, because the interval between the process request and the sheet supply increases, the first copy time also increases.
However, although the first copy time increases, because the increased time corresponds to the short time that is required to move from the staple replacement position to the home position, the conventional sheet processing device sets the specified Tw to either the time required to move from the staple replacement position or the time required to move from the home position. In the latter case, after the staple replacement, the sheet is supplied to the post-processing device after the specified time Tw after the stapler is automatically returned to the home position or a home-position return instruction is received via the control panel.
In the former case, the time required to move from the staple replacement position to the home position is always idle time. In the latter case, a longer time is required compared with the former case because a user operation is inserted after the staple replacement and before resuming the operation.